Morpho-physiological and yield contributing traits of cotton varieties with different tolerance to water deficit. Jaloliddin Shavkiev, Abdulahad Azimov, Shukhrat Khamdullaev Institute of Genetics and Plant Experimental Biology, Academy of Sciences of

Morpho-physiological and yield contributing traits of cotton varieties with different tolerance to water deficit.
Jaloliddin Shavkiev, Abdulahad Azimov, Shukhrat Khamdullaev
Institute of Genetics and Plant Experimental Biology, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan
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Abstract: Climate change and rising temperatures caused water deficites due to lesser and irregular rainfalls, leading to lower production of crops. Morpho-physiological and yield contributing traits of Upland (G. hirsutim L.) cotton varieties grown under optimal water supply (control) and water deficit (experimental) conditions are presented in the article, total chlorophyll, chlorophyll "a", chlorophyll "b", carotenoids, the amounts of proline, malonyldialdehyde, yield per plant, cotton weight per boll, the number of seeds per boll and the number of bolls per plant and the results of their correlation analysis are presented. Under water deficit conditions, there is a strong positive correlation between the carotenoids in plant leaves and the number of bolls per plant, a strong negative correlation between the amount of carotenoids and malonyldialdehyde, a strong negative correlation between malonyldialdehyde in plant leaves and the number of bolls per plant, a strong positive correlation between plant productivity and the number of bolls per plant was found to exist. It has been determined that the varieties of Ishonch and Navbahor-2 are more resistant to water deficit than C-6524 and Tashkent-6 in traits of physiological-biochemical and yield attributes.
Key words: G. hirsutum L., cotton, water deficit, varieties, physiology, morphology.


INTRODUCTION
Globally, increasing water and energy demand is expected to reach 6.9 trillion cubic meters by 2030, exceeding 40% of the available water supplies. The global climate changes observed in the world cause an increase in air temperature in the biosphere, and hot winds caused by a sharp decrease in relative humidity in the summer months’ cause atmospheric and soil dryness. In the present era, when the water problem is serious, the creation and implementation of water-saving agro-technologies, including the creation of cotton varieties resistant to soil and atmospheric drought and with a high coefficient of efficient use of water, water are considered the most urgent tasks of the world's cotton industry. Scientific research is being carried out to combine traditional genetic selection methods with physiological research to create modern varieties of cotton, which is one of the main agricultural crops in the world. In this regard, in addition to the medium-fiber cotton varieties that dominate the cotton area, using cotton gene pool sources with high fiber technological indicators and resistance to environmental stress factors, determining the reactions of cultivated cotton species to water scarcity in terms of morpho-biological characteristics of varieties, lines, and hybrids, and distinguishing resistant genotypes, special attention is paid to the development of drought-resistant genotypes. Cotton plant is a valuable technical crop cultivated in many regions of the world. This plant is also an industrial crop grown in developed and developing countries (Imran et al., 2011).
Cotton varieties of the medium-fiber G. hirsutum L. type are grown as the main field crop in 77 countries around the world, covering approximately 32.0 million hectares and growing in a variety of soil and climate conditions. The worldwide cotton trade is approximately 20.0 billion US dollars per year (Saranga et al., 2001). In the cotton sector, cotton ginning and processing plants, the textile industry, etc. are the main source of employment for millions of people and constitute a significant share of the gross domestic product of many countries such as Uzbekistan, Australia, Greece, India, China, and Pakistan (https://kun.uz., 2022; worldbank.org., 2020). Uzbekistan ranks fifth in the world in terms of cotton production and fourth in the export of cotton raw materials, so it is among the largest cotton-growing countries in the world. About 93 percent of the country's cotton fields are planted with medium-fiber cotton varieties (worldbank.org., 2020; www.trendingtopmost.com., 2021). Like other countries, Uzbekistan is facing severe drought problems due to a lack of irrigation water.
The main problem in the decline of cotton productivity is related to the lack of irrigation water. Therefore, the creation of new varieties that can withstand the conditions of water scarcity is one of the most urgent tasks facing cotton science. Current global climate change will exacerbate water scarcity in the future. Given that these changes will continue in the near future, water scarcity is becoming a serious obstacle to crop production worldwide. In this situation, the need to create varieties resistant to water deficit increases (Longenberger et al., 2006).
According to data, the global average temperature is expected to increase by 2 °C to 4 °C, and precipitation will decrease by 30%, which will have a strong negative impact on productivity and water resources in 2050 (Khalikova et al., 2009). Thus, drought is a major challenge for food security, which indicates the need to develop agricultural crop varieties that perform well under conditions of water scarcity (Ben-Asher et al., 2007; Almeselmani et al., 2015).
Water deficit are one of the factors that negatively affect the growth and development of plants and, in turn, productivity. Depletion of water resources absorbed by plant roots, as well as the large amount of energy spent on water absorption, directly affect cotton productivity in irrigated agriculture. Therefore, the study of the drought tolerance of the plant is one of the main issues for farmers in the field of cotton cultivation, as well as in many other fields of agricultural crops (Talskikh et al., 2009; Howard et al., 2001).
Some scientists argue that cotton is a drought-resistant crop. However, as a result of the drought, cotton, like other crops, has experienced a significant reduction in yield. Lack of water has a significant negative effect on the morpho-physiological characteristics and productivity of cotton (Pace et al., 1999; Patil et al., 2011). Some researchers have noted that a large genetic variation occurs in cotton under water shortage and high temperature conditions and that this variation is maintained by genetic factors (Khaidarova and Samiev.,1993; Shavkiev et al., 2019).
Currently, the characteristics of cotton resistance to drought, high temperatures, insects, pests, and diseases are being studied in conjunction with morpho-economic and physiological characters in the research on the creation of water deficit varieties ( Khamdullaev et al., 2021). For the effective selection of drought-resistant cultivars, management of genetic differentiation through various morpho-economic characters has been implemented (Nabiev et al., 2020; Shavkiev et al., 2020).
Water deficit is a factor that has a strong negative effect on the physiological mechanisms of cotton. Prolonged periods of drought can be fatal to the cotton plant. The highest level of water demand occurs during the flowering period, while this demand is relatively low during the early and late flowering stages. The loss of crop elements caused by permanent drought also results in a significant loss of productivity (Makamov et al., 2022).
The evolution of drought-resistant structures is important for understanding the diverse array of phenotypic traits studied under drought. Molecular biologists have developed transgenic approaches to identify drought tolerance genes (Sanaev et al., 2021).
As a response to water deficit conditions, at first, in very early periods, a sharp change in the direction of slowing down the process of the enlargement of the leaf plate was noted in the plant, but it is noted that the process of photosynthesis does not change significantly. Due to the slowing down of the process of enlargement of the leaf plate surface, the level of consumption of carbohydrates and energy in the process of metabolism in the tissues of the plant organism decreases, and it is estimated that the saved energy and nutrients can be directed to the root system. Thus, it was noted that the root system of the plant is less sensitive to the effects of drought when compared to the growth and development of the aboveground parts (Shavkiev et al., 2017).
It has been studied that the morpho-physiological characteristics of the plant in water deficit can be evaluated by the water-holding properties of the leaf, the leaf surface, the permeability of the leaf mouth, the size of the leaf mouth, and other indicators (Ashiralieva et al., 2023). Relative water content has been reported to be the most important measure of water status in plants (Rakhimova et al., 2023). A specific relationship between relative water content and seed cotton yield has been identified under drought conditions (Chorshanbiev et al., 2023). Water deficit-resistant genotypes reduce water loss by reducing leaf area and stomatal opening. Morphological and physiological traits considered the most effective criteria for identifying high-yielding genotypes under drought conditions include cell membrane stability index, chlorophyll "a," and relative water content (Matniyazova et al., 2023; Saidigani et al., 2022).
(Kar et al., 2005) tested five cotton hybrids for yield under water-stress conditions. Their findings indicate that this stress factor negatively affected the yield of all five stressed hybrids at the flowering stage, which was found to be more sensitive to drought than the vegetative stage of cotton.
(Kumari et al., 2005) studied the water deficit tolerance of 20 cotton cultivars. Among the 20 tested cultivars, it was concluded that three cultivars were resistant to water deficits based on the fact that they retained a high level of water content in the leaves, produced more bolls and biomass, and produced more cotton.
(Bajwa and Vories., 2006) studied the sensitivity of cotton genotypes to different irrigation regimes and noted that water deficits have a significant negative effect on the quality indicators of cotton fiber, especially during the period of fiber development, when the length of the fiber decreases and the formation process slows down under the influence of drought.
In the experiments of (Kuchkarov et al., 2009), the main stem length was shortened to 60-80 cm and the number of crop branches was reduced to 6-12 pieces in cotton plants under conditions of water deficit, crop element shedding and preservation up to 30%, and boll weight was 0-8 g. It was found that the length of fiber decreased by 0.5–4.0 mm, and the vegetation period was also shortened.
In the last stage of the flowering period in cotton plants, under the influence of a water deficit, the development of the bolls formed in the late periods slows down, the length of the fiber is shortened, the strength of the fiber's resistance to mechanical impact decreases, and the degree of shedding of the existing bolls increases. Especially during the first 16–20 days after the flowering period in the plant, the length of the fiber is greatly affected by the lack of water. In the period 3–4 days before the opening of the pods in the plant, that is, in the 25–30 days of the development of the pods, the water deficit has a significant negative effect on the strength of the resistance to mechanical impact of the fiber (Shavkiev et al., 2021).
It was observed that the number of joints forming flower buds in the plant bush is drastically reduced due to the drought that occurs during the period before the flowering period of the plant. It is also noted that water shortage causes an imbalance of phytohormones in the buds and pods of the cotton plant, which, in turn, decreases the yield (Shavkiev et al., 2021).
Optimizing the morphology, physiology, and metabolic processes of plant organs and cells is required to increase the productivity of agricultural crops. However, this approach can often reduce the plant's tolerance to water deficits. Different mechanisms of resistance and adaptation to water deficits have been formed in plants. In many cases, a water deficit reduces plant growth, leaf area development, and duration (Shavkiev et al., 2021; Shavkiev et al., 2019).
Plant stem height, root length, and their biomass; chlorophyll and proline content; photosynthetic rate; and drought response genes are reliable indicators of plant response to water stress (Shavkiev J et al., 2020).
Drought has been found to cause late flowering in cotton, delayed boll formation, reduced fiber number in bolls, and increased fiber softness in bolls (Shavkiev et al., 2019).
(Holliyev., 2009) discovered that when cotton varieties are given enough water, the activation of physiological and biochemical processes in their bodies occurs. However, the amount of water in the soil being higher or lower than the optimal level has a negative effect on the passage of the above processes, particularly in cases of water deficit, and the low amount leads to the premature opening of the cysts.
The purpose of the experiment is to study the comparative analysis of physiological and morpho-economic characteristics of upland cotton varieties with different resistance to water deficit and the correlation between the characteristics.